Will Winter Weather Help Protect Trees From Emerald Ash Borer?

The emerald ash borer (EAB) is not native to North America. Originally from Asia, it was first discovered on our continent in 2002 near Detroit, MI. Now, it has overtaken trees in at least 35 states and five Canadian provinces, including Ontario. It is an invasive species with few natural predators on this side of the world, though woodpeckers do enjoy feasting on them. As such, they have caused a lot of damage to ash trees in our region and beyond.

The Damage From the Emerald Ash Borer

The adult EAB is an iridescent, emerald green beetle that is approximately 1.25 cm in length. It lays minuscule reddish-brown eggs, from which flat-headed, white larvae hatch. The adults feed on the leaves of the tree, but the damage they do is relatively minor. It is the larvae that kill this valuable tree, and they’ve done so to tens of millions of trees in North America.

Female EAB lay their eggs in the spring. When the larvae hatch, they bore into the tree and spend the remainder of that stage under the tree’s bark. As they feed, they leave a noticeable trail behind them. When a tree becomes infested, the large numbers of this destructive insect disrupt the tree’s transport of nutrients and water. It is this damage that eventually kills the tree. Once an ash tree is taken over by the EAB, it generally dies within three to four years. Smaller trees may only make it half as long.

The Effects of Winter Weather

Canadian winters can get cold, and it can seem like all life should die off when exposed to some of the extreme temperatures we experience. So, how does the EAB fare in our cold climate? Unfortunately, it does quite well. Winter does not provide much in the way of protection from the unfettered growth of emerald ash borer population explosions. The larvae can survive in temperatures as low as negative 23-30 degrees Celsius. When it gets colder than that, they freeze.

Survival Mechanisms

Most insects that survive in colder climates have specific traits or behaviours that allow them to do so. The emerald ash borer is no different. One such trait is the fact that the larvae do not freeze until they reach minus 31 degrees Celsius. This is known as the supercooling point. Not all larvae survive the cold, but the fact that they don’t freeze until it gets extremely cold outside means that many of them will make it through our Canadian winters.

The reason they are able to survive the cold is that they produce special sugars, antifreeze proteins and alcohols in preparation for and during the winter months. In doing so, it lowers the temperatures that lead to the freezing of their internal fluids. As more individuals become acclimated to colder temperatures, the populations of EAB continue to grow.

Another mechanism for survival lies in the insect’s boring behaviour. The larvae live beneath the bark of the tree and form cells around them. This gives them a layer of insulation from the surrounding cold air and wind temperatures. If the tree gets any sun during the day, the warmth from the sun provides additional protection.

The Steps You Can Take

If you have ash trees on your property, you cannot count on the winter temperatures in Ontario to offer much protection from an EAB infestation. One of the species that eats the emerald ash borer is the woodpecker. If you notice that woodpeckers are paying particular attention to your ash trees, then it is time for you to do the same. Likewise, if you see the tell-tale D-shaped exit hole the adults make.

Contact professionals in tree care to help you assess your trees for the EAB and treat any of those infected. Martin’s Tree Service has the expertise and experience to take care of all your tree needs. Contact us today for more information on what we can do for you.